Butylacetate is prepared by the reaction of butanol with acetic acid by which water is produced besides butylacetate. The reaction is reversible and acidic catalysts are utilized to accelerate it. Mineral acids, especially sulfuric acid or, more recently, ion exchange resins (EP 066059, DE 3636754), or zeolites and so-called solid superacids, are utilized for this purpose.
According to the state-of-the-art processes (Petrochémia 1985, 25, 99), almost equilibrium composition is achieved in a reactor, and the resulting mixture is then distilled by means of a distillation column to separate a mixture, the composition of which is close to the composition of the butanol-butylacetate-water ternary azeotrope. The amount of the reaction water is not sufficient to distill all butylacetate in the mentioned form, therefore additional water must be added. The volume of the waste water to be subsequently treated is thus increased, which is one of the main disadvantages of the processes known in the art. The said steps are very often combined, i.e. the synthesis takes place directly in the distillation column reboiler. Separation of the organic phase from the water phase of the heterogeneous azeotrope prepares conditions for subsequent separation of butylacetate from butanol by distillation of the organic phase in another distillation column from which a mixture containing butanol, traces of dilute water and a small amount of butylacetate is withdrawn as distillate. This overhead product is recycled while butylacetate of purity usually up to 98% mass. is withdrawn as a bottom product. The separation of unreacted butanol from butylacetate is very difficult because of strong nonideality of the mixture. Not only butanol, butylacetate and water create a ternary azeotrope with minimum boiling point but also butanol with butylacetate as well as butanol with water create binary azeotropes. The water phase separated from the first column distillate is further distilled by use of another distillation column, dissolved butanol and butylacetate being separated as distillate, this mixture being recycled to the process. Complex separation of the esterification reaction mixture components is the main disadvantage of the state-of-the-art processes. There are also serious corrosion problems as an additional disadvantage in those processes which utilize mineral acids as catalysts.
Another variant of the butylacetate synthesis makes it possible to perform the reaction in a column-reactor packed with the ion-exchange catalyst arranged into two zones (CN 1107136A). There is a partial condenser placed into the column head. The vapors are partly condensed in the condenser, the distillate being refluxed to the upper reaction zone without being split into water and organic phases. This has a bad impact on the reaction equilibrium, which is a considerable disadvantage of said system. The vapors, non-condensed in the partial condenser, built in the column head, condense in an external condenser, the condensate being refluxed into the column feed after separation of the water from the organic phases, so the problem of accumulation of low boiling impurities in the upper part of the column remains unsolved. The product is withdrawn from the bottom of the reactor. Maximum purity is only 95 to 98 mass. % according to said patent (CN 1107136A).
Isobutylacetate is prepared by the reaction of isobutyl alcohol with acetic acid by which water is produced besides isobutylacetate. The reaction is reversible, and acidic catalysts are utilized to accelerate it. Mineral acids, especially sulfuric acid or, more recently, solid acidic catalysts, are utilized for this purpose as can be seen e.g. from CZ 191357 and CZ 279562. These catalysts can be ion exchange resins, zeolites, so-called solid superacids and the like.
According to the state-of-the-art processes relating to isobutylacetate preparation, almost equilibrium composition is achieved in a reactor, the composition being dependent on the starting molar ratio of the reaction components. The resulting mixture is then distilled by means of a distillation column to separate a mixture, the composition of which is close to the composition of the isobutyl alcohol-isobutylacetate-water ternary azeotrope. The amount of reaction water is not sufficient to distill all isobutylacetate in the mentioned form, therefore additional water must be added to the mixture. The volume of the waste water to be subsequently treated is thus increased, which is one of the main disadvantages of the processes known in the art. Said steps are very often combined, i.e. the synthesis takes place directly in the distillation column reboiler. After separating the organic phase from the water phase of the heterogeneous azeotrope it is possible to separate isobutylacetate from isobutyl alcohol by subsequent distillation of the organic phase in another distillation column. The organic phase, separated from the heterogeneous azeotropic mixture, contains isobutyl alcohol, isobutylacetate and a certain part of water. Isobutyl alcohol, the rest of the water and a small part of isobutylacetate are separated from said organic phase by subsequent distillation. The overhead product, obtained this way, is recycled into esterification while pure isobutylacetate is withdrawn as a bottom product. The separation of unreacted isobutyl alcohol from isobutylacetate is very difficult because of strong nonideality of the mixture. Isobutyl alcohol and isobutylacetate create a binary azeotrope, creating also a ternary azeotrope of a minimum boiling point with water. The water phase separated from the distillate of the first column is further distilled by means of another distillation column, dissolved isobutyl alcohol and isobutylacetate being separated overhead, their mixture being recycled to the process. Complex separation of the esterification reaction mixture components is the main disadvantage of these state-of-the-art processes. There are also serious corrosion problems as an additional disadvantage in those processes which utilize mineral acids as catalysts.